Measurement Computing 6224 - Manual (Page 29)

7-4 Strain and Pressure/Force 6224 User’s Manual
Quarter-Bridge II
Quarter-bridge type II measures either axial or bending strain.
Quarter-bridge type II has the following characteristics:
One active strain-gauge element and one passive, temperature-sensing quarter-bridge element (dummy gauge). The
active element is mounted in the direction of axial or bending strain. The dummy gauge is mounted in close thermal
contact with the strain specimen but not bonded to the specimen, and is usually mounted transverse (perpendicular)
to the principle axis of strain.
This configuration is often confused with the half-bridge type I configuration, with the difference being that in the
half-bridge type I configuration the R3 element is active and bonded to the strain specimen to measure the effect of
Poisson’s ratio.
Completion resistors provide half bridge completion.
Compensates for temperature.
Sensitivity at 1000 is ~ 0.5 mV
out
/ V
EX
input.
The following symbols apply to the above circuit diagram and to the equations provided in the supplemental information.
R1 and R2 are half-bridge completion resistors.
R3 is the quarter-bridge temperature-sensing element (dummy gauge).
R4 is the active strain-gauge element measuring tensile strain (+ ).
Supplemental Information
Data from strain channels (Quarter-Bridge II) is converted to strain units using the following equation:
10
6
4 V r
GF 1 2 V r
1
R L
R g